Force run nixos-upgrade if device was offline

configuration.nix

@@ -55,6 +55,9 @@ in {
   systemd.services.nixos-upgrade.serviceConfig.ExecStartPre =
     "${pkgs.nix}/bin/nix-channel --update";
 
+  # force run if device was offline
+  systemd.timers.nixos-upgrade.timerConfig.Persistent = true;
+
   system.stateVersion = "19.03";
   system.autoUpgrade.enable = true;